On a whim, at age 23, Jesús Castillo bought a pack of index cards, and for the next two years carried a small stack of them wherever he went. The cards provided the form for a long serial poem called Remains, which was recently published by McSweeney’s.

“I filled them out whenever something (a sight or a moment) inspired a line,” he said by email. “After the first line, I would fill out the rest of the card, going by instinct as much as possible, without pausing or pausing as little as possible. Each filled-out card became a stanza in the poem (though I didn’t keep all of the stanzas). When the space on the card ended, the stanza ended. I had no writing schedule. I just filled out cards whenever I was moved to do so. A lot of the stanzas were written in transit.”

Born in San Luis Potosi, Mexico, in 1986, Castillo moved to California in 1998 and graduated from UC San Diego in 2009. The following year, he moved to Oakland, where he helped form ’Lectric Collective and started the journal Vertebrae. After finishing “Remains,” he left for Iowa, where he earned a master’s degree in 2015.

Speaking by phone from Santa Fe, where he works in a domestic violence shelter and counseling center, he described the process of writing the poem as “being attentive to as much as possible all the time,” and the poem itself as “records of moments, and then meditations inside of those moments.” Memories emerge from and define observations, forming a timeless epic that seems at once all-encompassing and utterly infinite. Every page is self-contained, but so concentrated as to indicate beyond itself. For example:

“The delicately crazy wander their workplaces/ with a smile on and always a task to carry out, their minds/ full of knives and fears and a need to be needed. I wish/ I was better at inciting in people a lightheartedness./ That I was better at laughter. At my job there is a middle-/ aged woman who acts like a child. She must/ have her reasons. She said, once, in casual/ conversation, that she didn’t want to die. She would/ miss everyone. No, you won’t, someone/ corrected her.”

In tone, the book has an elegaic quality. But as much as the title invokes a sense of what is left behind, it also suggests a coalescence, or a longing to answer the question of what remains to be done.

“The elegy is just one mode in which to begin to make connections,” Castillo said. “It’s not the only one. The value is in whether or not the poem heightens your perception of things, or makes you somehow more aware.” He references Nietzsche’s statement in “The Will to Power” that “the effect of works of art is to excite the state that creates art.”

“If it makes connections that are insightful and invigorating,” Castillo said, “that’s good.”